This invention relates to two speed accessory drives and is related to my prior filed, commonly assigned patent application entitled "Differential Drive Mechanism", U.S. Pat. No. 4,484,495 issued Nov. 27, 1984. In the above noted application there was proposed a differential drive mechanism utilizing a planetary gear and an electromagnetic clutch to provide a two speed driving mechanism for engine accessories which provides for increased engine fuel economy and increased acceleration performance. This mechanism permitted engine driven belt accessories to be driven at a high drive ratio during engine idle and at a lower drive ratio during highway cruise conditions or when the vehicle is accelerated. In this manner the parasitic drag inherent with these belt driven accessories is reduced, thus improving engine and vehicular performance. The present invention provides the above features and advantages and further reduces the torque transmitting requirement at the friction surface yielding a further improvement in performance and further reducing the torque transmitted by and across the planet or pinion gear of the planetary gear set.
According to the specific embodiment described in detail below, the present invention comprises a two speed drive comprising: a driving member; a rotable driven member coaxially positioned relative to the driving member; planetary gear means rotatable with the driving member and with the driven member for providing in one condition a non-reducing speed drive and providing in a second condition a speed reducing drive therebetween, the gear means including a sun gear drivingly engaging the driving member, a ring gear mounted for rotation about said driving member, and a plurality of planetary gears interconnecting said sun gear and the ring gear, the driven member attached to and carried with the planetary gears; and electromagnetic clutch means, operable in a first mode for simultaneously driving the sun gear and the ring gear in the one condition to establish a non-reducing speed drive and operable in a second mode to rotationally lock the ring gear for driving the driven member through the sun gear and the planetary gears at a speed less than the speed of the driving members.
Many other objects, features and advantages of the invention will be clear from the detailed description of the drawings.